Polyamic acid resin composition

ABSTRACT

Provided is a polyamic acid resin composition for formation of a bank, which provides excellent film characteristics and adhesion to a substrate, which can undergo patterning with use of a positive type photoresist, and which can be transformed into a polyimide after the patterning to yield a polyimide resin with upper part of film having a low surface energy. It is achieved by a polyamic acid resin composition comprising a polyamic acid [a] as a base and a polyamic acid [b] having a fluorine-containing alkyl group with a carbon number of at least 2, and containing the polyamic acid [b] in an amount of from 0.1 to 30 wt % to the total amount of the polyamic acid [a] and the polyamic acid [b].

TECHNICAL FIELD

The present invention relates to a polyamic acid resin composition forformation of a bulkhead to separate pixels from each other in liquidcrystal displays, EL displays, and the like. More particularly, thepresent invention relates to a polyamic acid resin composition capableof forming a polyamic acid resin film, followed by patterning thereofwith use of a positive type photoresist, and thereafter being imidizedto obtain a polyimide resin bulkhead with a low surface energy property.

This polyamic acid resin composition is suitable for use as a lightshielding material and a bulkhead material adapted to the ink jetmethod, in the liquid crystal displays and EL displays.

Display apparatus for various displays using liquid crystal displaydevices or organic EL display devices, has achieved remarkabledevelopment thanks to its excellent properties of small size, lightweight, and low electric power consumption.

In recent years, lively investigation has been made on manufacturingtechnologies using the ink jet method in production of these displays.For example, for producing a color filter in the liquid crystal displaydevice, a method proposed is a color filter production process wherein apreliminarily patterned bulkhead (hereinafter referred to as a “bank”)to define pixels is made of a light-shielding photosensitive resin layerand ink droplets are dropped into each aperture enclosed with the bank,in contrast to the conventional printing method, electrodepositionmethod, staining method, or pigment-dispersion method. Furthermore, inthe case of the organic EL display devices, a proposal was also made ona method for production of the organic EL display devices wherein thebank was preliminarily formed and ink droplets were dropped similarly toform luminescent layers.

In dropping the ink droplets into the apertures enclosed with the bankby the ink jet method, in order to prevent the ink droplets from flowingover the bank into adjacent pixels, it is necessary to provide asubstrate with affinity for ink and the surface of the bank with inkrepellency. Furthermore, if the side face of the bank has too high inkrepellency, there will also arise the problem that the ink layers becometoo thin in the vicinity of the bank.

JP-A-2000-187111 suggests a method of preparing the bank material in alaminated structure of a metal film and a photosensitive organic thinfilm, and blending a fluorochemical surfactant and a fluorinated polymerexcept for polyimides into the photosensitive organic thin film, so asto make the surface of the photosensitive organic thin film have a lowsurface energy; and a method of performing a continuous plasma treatmentwith oxygen gas and with fluoride gas to provide the substrate withaffinity for ink and the bank with ink repellency. However, the methodof blending the fluorochemical surfactant and the fluorinated polymerexcept for polyimides into the photosensitive organic thin film involvedmany points to be considered, including compatibility and amounts to beadded, as well as both photosensitivity and film characteristics, andthe method of performing the continuous plasma treatment requiredcomplicated steps; therefore, they were hardly practical.

The present invention has been accomplished under the abovecircumstances, and it is an object of the present invention to provide apolyamic acid resin composition, which provides excellent filmcharacteristics and adhesion to a substrate, which can undergopatterning with use of a positive type photoresist, and which can betransformed into a polyimide after the patterning to yield a polyimideresin with upper part of film having a low surface energy.

DISCLOSURE OF THE INVENTION

The present inventors have conducted elaborate study to overcome theabove problems, and, as a result, have accomplished the presentinvention.

Namely, the present invention provides a polyamic acid resin compositionfor formation of a bank, which comprises a polyamic acid [a] havingrepeating units represented by the following formula (1):

(wherein R¹ is a tetravalent organic group constituting atetracarboxylic acid or a derivative thereof, R² is a bivalent organicgroup constituting a diamine, and k is an integer) and having a reducedviscosity of from 0.05 to 5.0 dl/g (in N-methylpyrrolidone at atemperature of 30° C., at a concentration of 0.5 g/dl); and

a polyamic acid [b] having repeating units represented by the followingformula (2):

(wherein R³ is a tetravalent organic group constituting atetracarboxylic acid or a derivative thereof, R⁴ is a bivalent organicgroup constituting a diamine, from 1 to 100 mol % of R⁴ has one or morefluorine-containing alkyl groups with a carbon number of at least 2, and1 is an integer), and having a reduced viscosity of from 0.05 to 5.0dl/g (in N-methylpyrrolidone at a temperature of 30° C., at aconcentration of 0.5 g/dl);

wherein the content of the polyamic acid [b] is from 0.1 to 30 wt % tothe total amount of the polyamic acid [a] and the polyamic acid [b].

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be explained in detail.

The polyamic acid resin composition of the present invention is acomposition comprising a polyamic acid [a] as a base and a polyamic acid[b] having a fluorine-containing alkyl group.

The polyamic acid [b] has the fluorine-containing alkyl group whereby itcomes to have a low surface energy and to demonstrate the ink repellencyin the form of the bank.

<Polyamic Acid [a]>

The polyamic acid [a], which is a component of the polyamic acid resincomposition of the present invention, is a polyamic acid havingrepeating units represented by the above-stated formula (1).

Although there are no particular restrictions on a method of producingthe polyamic acid, it can generally be obtained by reacting orpolymerizing a diamine with a tetracarboxylic acid or its derivative,e.g. a tetracarboxylic dianhydride, or with a dicarboxylic aciddihalide, or the like. Furthermore, a method usually applicable is oneof reacting or polymerizing a diamine with a tetracarboxylic dianhydride(hereinafter abbreviated to “acid dianhydride”), in a polar solvent suchas N-methylpyrrolidone.

There are no particular restrictions on the diamine used for obtainingthe polyamic acid [a], and it is possible to use a single diamine, or touse two or more diamines simultaneously.

Particularly, specific examples of the diamine includep-phenylenediamine, m-phenylenediamine,4,4-methylene-bis(2,6-ethylaniline),4,4′-methylene-bis(2-isopropyl-6-methylaniline),4,4′-methylene-bis(2,6-diisopropylaniline),2,4,6-trimethyl-1,3-phenylenediamine,2,4,5,6-tetramethyl-1,4-phenylenediamine, o-toluidine, m-toiuidine,3,3′, 5,5′-tetramethylbenzidine, bis[4-(3-aminophenoxy)phenyl]sulfone,2,2-bis[4-(3-aminophenoxy)phenyl]propane,2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane, 4,4′-diamino-3 3′-dimethyldicyclohexylmethane, 4,4′-diaminodiphenyl ether,3,4-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane,2,2-bis(4-anilino)hexafluoropropane,2,2-bis(3-anilino)hexafluoropropane,2,2-bis(3-aniino-4-toluyl)hexafluoropropane,1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,bis[4-(4-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane and2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

Furthermore, in order to increase the adhesion to the substrate, it isalso preferable to use a diamine containing siloxane.

Specific examples of the siloxane-containing diamine are as follows:

(wherein p is an integer from 1 to 10).

There are no particular restrictions on the acid dianhydride applicablefor obtaining the polyamic acid [a], and it is possible to use a singleacid dianhydride, or to use two or more acid dianhydridessimultaneously.

Particularly, specific examples of the acid dianhydride include aromatictetracarboxylic dianhydrides such as pyromellitic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-diphenylether tetracarboxylic dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and3,3′,4,4′-diphenyl sulfone tetracarboxylic dianhydride.

Further specific examples of the acid dianhydride include alicyclictetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride,2,3,5-tricarboxy-2-cyclopentaneacetic dianhydride,bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, and3,5,6-tricarboxy-2-norbornaneacetic dianhydride, and aliphatictetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylicdianhydride.

In view of solubility of the polyamic acid resin film to an alkalideveloper, the acid dianhydride is preferably one comprised of atetracarboxylic acid wherein the four carbonyl groups are not directlybonded to an aromatic ring, such as 1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylicdianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride,2,3,5-tricarboxy-2-cyclopentaneacetic dianhydride,bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, and3,5,6-tricarboxy-2-norbornaneacetic dianhydride, and is more preferably1,2,3,4-cyclobutanetetracarboxylic dianhydride.

On the occasion of the polymerization of the polyamic acids, a ratio ofthe total mole of the diamine and that of the tetracarboxylicdianhydride is preferably from 0.8 to 1.2.

The closer to 1 the molar ratio, the higher the polymerization degree ofthe polymer to be produced, as being the case in ordinary condensationpolymerization reaction. If the polymerization degree is too low, thestrength of the film will be inadequate. If the polymerization degree istoo high, workability during formation of the film will be poor incertain cases. Accordingly, the polymerization degree of the product inthe present invention is preferably such that the reduced viscosity isfrom 0.05 to 5.0 dl/g (in N-methylpyrrolidone at a temperature of 30°C., at a concentration of 0.5 g/dl). The above reduced viscosity isparticularly preferably from 0.2 to 2.0 dl/g in the above range.

Specific examples of the polar solvent applicable in reacting thediamine with the acid dianhydride in the polar solvent includeN,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone,N-vinylpyrrolidone, N-methylcaprolactam, dimethylsulfoxide,tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide,m-cresol, and γ-butyrolactone. They may be used alone or as a mixture.Furthermore, it is also possible to use a solvent that does not dissolvethe polyamic acid if it is used as mixed in the above solvent within arange in which the polyamic acid formed by the polymerization does notprecipitate.

Furthermore, the diamine is reacted with the acid dianhydride at areaction temperature optionally selected from the range of from −20 to150° C., and preferably from the range of from −5 to 100° C.

The polyamic acid thus obtained can be used as it is, or can be usedafter a process of precipitating and isolating the polyamic acid in apoor solvent such as methanol, ethanol, or the like, and collecting it.

<Polyamic Acid [b]>

The polyamic acid [b], which is a component of the polyamic acid resincomposition of the present invention, is a polyamic acid havingrepeating units represented by the above formula (2).

There are no specific restrictions on a method for producing thepolyamic acid, and it can be obtained in much the same manner as theabove polyamic acid [a] was.

The reduced viscosity of the polyamic acid [b] is preferably in a rangeof from 0.05 to 5.0 dl/g (in N-methylpyrrolidone at a temperature of 30°C., at a concentration of 0.5 g/dl), for the same reason as that of thepolyamic acid [a], and more preferably in a range of from 0.1 to 1.5dl/g. In this connection, if the reduced viscosity of the polyamic acid[b] is set to be smaller than that of the polyamic acid [a], thepolyamic acid [b] tends to be locally distributed more in the vicinityof the surface of the film formed from the polyamic acid resincomposition of the present invention, which is more preferable.

The diamine used for obtaining the polyamic acid [b] may be a singlediamine or be two or more diamines used simultaneously, but it isnecessary to use at least one diamine having a fluorine-containing alkylgroup with a carbon number of at least 2, in order to impart the lowsurface energy property to the polyamic acid [b].

There are no specific restrictions on the diamine having thefluorine-containing alkyl group with the carbon number of at least 2,and the diamine may be preferably a diamine having a fluorine-containingalkyl group with a carbon number of at least 6, and more preferably adiamine having a fluorine-containing alkyl group with a carbon number offrom 8 to 20. The number of fluorine-containing alkyl groups can be oneor more per diamine.

Generally, with increase in the number of carbon atoms in thefluorine-containing alkyl group, and with increase in the number offluorine-containing alkyl groups per diamine, the effect of lowering thesurface energy becomes more significant.

Specific examples of the diamine having the fluorine-containing alkylgroup with the carbon number of at least 2 include diamines having thefluorine-containing alkyl group, such as4-trifluoroethyl-1,3-diaminobenzene,4-perfluorohexyl-1,3-diaminobenzene,4-perfluorooctyl-1,3-diaminobenzene,4-perfluorodecyl-1,3-diaminobenzene,5-(2,2,3,3,3-pentafluoropropyl-1-oxymethyl)-1,3-diaminobenzene,5-(1H,1H,2H,2H-heptadecafluorodecyl-1-oxymethyl)-1,3-diaminobenzene,4-perfluorodecyl-1,3-diaminobenzene,2,2,3,3,3-pentafluoropropyl-3,5-diaminobenzoate,1H,1H,2H,2H-heptadecafluorodecyl-3,5,-diaminobenzoate, and4-(4-perfluorooctylphenoxy)-1,3-diaminobenzene. However, the presentinvention is not limited to those.

The diamine used for obtaining the polyamic acid [b] may be only thediamine having the fluorine-containing alkyl group with the carbonnumber of at least 2, and may contain another diamine as mixed thereto.In this case, the amount of the diamine having the fluorine-containingalkyl group with the carbon number of at least 2 is preferably from 1 to100 mol % relative to the total mols of all the diamines used, andparticularly preferably from 25 to 75 mol %. If the amount of thediamine having the fluorine-containing alkyl group with the carbonnumber of at least 2 is less than 1 mol %, the effect of reducing thesurface energy might be inadequate in some cases. In addition, when theother diamine is mixed in an amount of at least 25 mol %, it is expectedto enhance the compatibility of the polyamic acid [b] with the polyamicacid [a] in a solution state and the stability of the polyamic acidresin composition of the present invention.

There are no specific restrictions on the above “other diamine,” andspecific examples thereof correspond to the specific examples of thediamine that can be used for obtaining the polyamic acid [a].

There are no specific restrictions on the acid dianhydride used forobtaining the polyamic acid [b], and it is possible to use a single aciddianhydride, or to use two or more acid dianhydrides simultaneously.

Particularly, specific examples of the acid anhydride correspond to thespecific examples of the acid dianhydrides that can be used forobtaining the polyamic acid [a]. Namely, just as in the case of thepolyamic acid [a], from the viewpoint of the solubility of the polyamicacid resin film to the alkali developer, the acid dianhydride ispreferably one comprised of a tetracarboxylic acid wherein the fourcarbonyl groups are not directly bonded to an aromatic ring, such as1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride,2,3,5-tricarboxy-2-cyclopentaneacetic dianhydride,bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, or3,5,6-tricarboxy-2-norbornaneacetic dianhydride, and is more preferably1,2,3,4-cyclobutanetetracarboxylic dianhydride.

<Polyamic Acid Resin Composition>

The polyamic acid resin composition of the present invention containsthe aforementioned polyamic acid [a] and polyamic acid [b], and isusually used in the form of a solution in which the composition isdissolved in an organic solvent.

There are no specific restrictions on the above organic solvent as longas the polyamic acid [a] and the polyamic acid [b] can be dissolveduniformly therein.

Specific examples of the solvent include N,N-dimethylformamide,N,N-dimethylacetamide, N-methylpyrrolidone, N-vinylpyrrolidone,N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, pyridine,dimethylsulfone, hexamethylsulfoxide, m-cresol, and γ-butyrolactone.

Furthermore, depending on objectives such as the coating property andthe printing property onto the substrate, the storage stability, and thelike, another organic solvent may be mixed unless it inhibits thedissolution of the resin components. Specific examples of the additionalorganic solvent include ethyl cellosolve, butyl cellosolve, ethylcarbitol, butyl carbitol, ethyl carbitol acetate, butyl carbitolacetate, ethylene glycol, ethyl lactate, butyl lactate, cyclohexanone,and cyclopentanone.

There are no specific restrictions on the resin concentration in thesolution as long as the resin is uniformly dissolved in the organicsolvent, and it is preferably in a range of from 1 to 50 wt % from theviewpoint of tractability.

Although the compounding ratio of the polyamic acid [a] and the polyamicacid [b] can be optionally selected for controlling the surface energyof the film, it is limited in the polyamic acid resin composition of thepresent invention for the following reasons.

With use of only the polyamic acid [a], the surface energy of the bankformed thereof will not be low enough, so that the ink repellency willbe inadequate. On the other hand, with use of only the polyamic acid[b], the adhesion to the substrate might be inadequate, and the sideface of the bank will also have the surface energy too low to secure asufficient coating property of ink on the side face of the bank in somecases.

When a film is formed from the solution of the resin compositioncontaining the polyamic acid [a] and the polyamic acid [b], the polyamicacid [b] having the low surface energy is locally distributed in thevicinity of the surface of the film. When this film is subjected toetching to form a bank, the resultant bank has a low surface energy onlyin the upper part.

At this time, if the compounding amount of the polyamic acid [b] is toosmall, the upper part of the bank will fail to have a sufficiently lowsurface energy; whereas if the compounding amount is too large, even theside face of the bank will have a low surface energy as well.

Accordingly, the content of the polyamic acid [b] in the polyamic acidresin composition of the present invention is from 0.1 to 30 wt %,preferably from 0.1 to 10 wt. %, and more preferably from 0.1 to 5 wt %,to the total amount of the polyamic acid [a] and the polyamic acid [b].

If the content of the polyamic acid [b] is too large, the coatingproperty of the solution will become poor in some cases.

The polyamic acid resin composition of the present invention can beobtained by mixing the aforementioned polyamic acid [a] and polyamicacid [b] in an organic solvent, or by mixing solutions of the respectivepolyamic acids [a] and [b].

For forming the bank from the polyamic acid resin composition of thepresent invention, the solution is first applied onto a substrate, suchas an ITO film-coated glass substrate, a SiO₂-coated glass substrate, ora Cr film-coated glass substrate, by spin coating, and preliminarydrying is conducted at a temperature of from 50 to 130° C. to form afilm. On this occasion, it is, of course, preferable to use a substratetreated with a silane-based coupling agent.

Then the pre-dried film is baked again at an appropriate temperature tocontrol alkali solubility (called β-bake); a positive type resist isapplied onto the film; light is irradiated onto the film through a maskhaving a predetermined pattern; the resist and film are developed withan alkali developer, whereby not only the exposed part of the resist butalso the exposed part of the polyamic acid resin are washed out to leavea relief pattern with a sharp end face.

The temperature of the β-bake is an appropriate temperature generallyselected in a range of from 150° C. to 200° C., depending on thestructures of the polyamic acids. If the β-bake temperature is too high,the alkali solubility will be insufficient in the exposed part of thepolyamic acid resin. If the β-bake temperature is too low, the polyamicacid resin will also be dissolved in the unexposed part. Thus thetemperature setting outside the above temperature range will fail toobtain a good relief pattern in either case.

The positive type photoresist may be any commercially availablephotoresist that is sensitive to the i-line or the g-line, with noparticular restrictions.

A light source used is generally a very high pressure mercury lamp, anda spectroscopic filter is interposed between the light source and themask to implement spectral irradiation with the i-line (365 nm), theh-line (405 nm), the g-line (436 nm), or the like. The film obtainedfrom the polyamic acid resin composition of the present invention can bepatterned with light of either of these wavelengths.

Furthermore, a method for transferring the mask pattern onto the filmcan, for example, be contact exposure with a contact aligner, proximityexposure, reduction projection exposure with a stepper.

The developer used in the development may be any alkali aqueoussolution, and specific examples thereof include aqueous solutions ofalkali metal hydroxides such as caustic potash, and caustic soda,aqueous solutions of quaternary ammonium hydroxides such astetramethylammonium hydroxide, tetraethylammonium hydroxide, andcholine, and solutions of amines such as ethanolamine, propylamine,ethylenediamine. In addition, a surfactant can be added into thedeveloper.

These developers can be used at from 5 to 50° C., and the film obtainedfrom the polyamic acid resin composition of the present invention has ahigh solubility in the exposed part and can readily be developed at roomtemperature with 2.38 wt % general-purpose tetramethylammoniumhydroxide.

The resist remaining on the unexposed portion can be easily removed byimmersing it in the solvent used for dissolving the resist.Particularly, specific typical examples of the solvent include propyleneglycol, propylene glycol monoethyl ether, 2-heptane, cyclohexanone.

The substrate with the relief pattern obtained as described above, issubjected further to a heat treatment at from 200° C. to 300° C. tocomplete imidization, thereby obtaining a satisfactory bank having thelow surface energy only in the upper part and having excellent heatresistance, chemical resistance, and electrical characteristics, whichare the characteristics of polyimide.

In order to impart the satisfactory ink repellency to the upper part ofthe bank obtained as described above, after the removal of the resist inthe unexposed part and the thermal imidization, the upper part of thefilm has the surface energy of preferably at most 35 dyn/cm, andparticularly preferably at most 30 dyn/cm; or it has the contact anglewith water of preferably at least 80°, and particularly preferably atleast 95°.

In view of the affinity to the alkali developer on the occasion of thedevelopment after the exposure, the above surface energy is preferablyat least 10 dyn/cm, and the contact angle with water is preferably atmost 150°.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted by such specific Examples.

EXAMPLE 1

Production of Polyamic Acid Resin Composition

10.00 g (34.2 mmol) of 1,3-bis(4-aminophenoxy)benzene, 0.44 g (1.8 mmol)of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and 7.06 g(36.0 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride were madeto react in 96.6 g of N-methylpyrrolidone (hereinafter abbreviated toNMP in some cases) at room temperature for six hours, to obtain asolution of a polyamic acid [a-1] having a number average molecularweight of 40,000 (k=82 as repeating units). The reduced viscosity of thepolyamic acid was 1.0 dl/g (in N-methylpyrrolidone at a temperature of30° C., at a concentration of 0.5 g/dl).

Furthermore, 1.20 g (4.1 mmol) of 1,3-bis(4-aminophenoxy)benzene, 1.10 g(2.0 mmol) of 4-(4-perfluorooctylphenoxy)-1,3-diaminobenzene, and 1.20 g(6.1 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride were madeto react in 19.8 g of N-methylpyrrolidone (hereinafter abbreviated toNMP) at room temperature for six hours, to obtain a solution of apolyamic acid [b-1] having a number average molecular weight of 10,000(l=17 as repeating units). The reduced viscosity of the polyamic acidwas 0.4 dl/g (in N-methylpyrrolidone at a temperature of 30° C., at aconcentration of 0.5 g/dl).

0.2 g of the solution of the above polyamic acid [b-1] (solid contentratio=99:1) was added into 20 g of the solution of the above polyamicacid [a-1] and 5.0 g of NMP was further added thereinto to dilute thesolution to a resin concentration of 12%. This solution was stirred atroom temperature for one hour to obtain a uniform solution. Theresultant mixture was filtered by a 0.4 μm filter to obtain a solutionof the polyamic acid resin composition of the present invention.

(Pattern Formation)

This polyamic acid resin solution was directly applied onto anSiO₂-coated glass substrate by means of a spin coater, and the substratewas heated at 90° C. on a hot plate for three minutes, thereby obtaininga uniform film 2.3 μm thick. Then the substrate was subjected to theβ-bake at 170° C. on the hot plate for three minutes, and a positivetype photoresist for the g-line S-1808 (manufactured by SHIPLEY Company)was applied up to a film thickness of 1.0 μm. This film was exposedthrough a test mask to entire ultraviolet light at a dose of 1000 mJ/cm²by an ultraviolet irradiation system (PLA-501 manufactured by CanonInc.). After the exposure, the substrate was immersed in an alkalideveloper (NMD-3 manufactured by TOKYO OHKA KOGYO CO., LTD) at 23° C.for 20 seconds to effect development, followed by a rinse with purewater for 20 seconds. After the resist was removed, it was confirmedthat a pattern was formed in the unexposed portions. The patternresolution was such that the line-and-space pattern was formed withoutpeeling up to the width of 10 μm. The film thus obtained was heated at250° C. in a circulating drying furnace for one hour, thereby obtaininga polyimide pattern 2.0 μm thick.

(Evaluation of Surface Energy)

The polyamic acid resin solution was directly applied onto anSiO₂-coated glass substrate by the spin coater, and the substrate washeated at 90° C. on the hot plate for three minutes, thereby obtaining auniform film 2.3 μm thick. Then the substrate was subjected to theβ-bake at 170° C. on the hot plate for three minutes, and the positivetype photoresist for the g-line S-1808 (manufactured by SHIPLEY Company)was applied up to a film thickness of 1.0 μm. A half of the film wasexposed through a mask to entire ultraviolet light at a dose of 1000mJ/cm² by the ultraviolet irradiation system (PLA-501 manufactured byCanon Inc.). After the exposure, the substrate was immersed in thealkali developer (NMD-3 manufactured by TOKYO OHKA KOGYO CO., LTD) at23° C. for 20 seconds to effect development, followed by a rinse withpure water for 20 seconds. After the resist was removed, the film thusobtained was heated at 250° C. for one hour in the circulating dryingfurnace, thereby obtaining a uniform polyimide film 2.0 μm thick.Contact angles with water and with methylene iodide on this film weremeasured and were 95° and 63°, respectively. Furthermore, the surfaceenergy of the film was determined based on the following calculation.(1+cos θ)×γ_(L)=2(γ_(S) ^(d)×γ_(L) ^(d))^(1/2)+2(γ_(S) ^(p)×γ_(L)^(p))^(1/2)γ_(L)=γ_(L) ^(d)+γ_(L) ^(p)γ_(S)=γ_(S) ^(d)+γ_(S) ^(p)

θ; contact angle of liquid on the film

γ_(L); surface energy of liquid

γ_(L) ^(d); disperse component of surface energy of liquid

γ_(L) ^(p); polar component of surface energy of liquid

γ_(S); surface energy of the film

γ_(S) ^(d); disperse component of surface energy of the film

γ_(S) ^(p); polar component of surface energy of the film.

Here, by letting the contact angle of water be θ₁, and the contact angleof methylene iodide be θ₂, and by putting the surface energies of water(γ_(L)=72.8, γ_(L) ^(d)=29.1, γ_(L) ^(p)=43.7) {dyn/cm} and the surfaceenergies of methylene iodide (γ_(L)=50.8, γ_(L) ^(d)=46.8, γ_(L)^(p)=4.0) {dyn/cm} into the above formulas, we obtain(1+cos θ₁)×72.8=2(γ_(S) ^(d)×29.1)^(1/2)+2(γ_(S) ^(p)×43.7)^(1/2) and(1+cos θ₂)×50.8=2(γ_(S) ^(d)×46.8)^(1/2)+2(γ_(S) ^(p)×4.0)^(1/2).Then θ₁ and θ₂ are replaced by measured values and the abovesimultaneous equations are solved to determine γ_(S) ^(d) and γ_(S)^(p).

As a result, the surface energy of the film was 27.3 dyn/cm.Furthermore, the SiO₂ substrate in the exposed part had the contactangles with water and with methylene iodide of 40.7° and 6.9°,respectively, and the surface energy of 58.9 dyn/cm.

EXAMPLE 2

0.61 g of the solution of the polyamic acid [b-1] was added into 20 g ofthe solution of the polyamic acid [a-1] (solid content ratio=97:3), and5.14 g of NMP was further added thereinto to dilute the solution to aresin concentration of 12%. This solution was stirred at roomtemperature for one hour to obtain a uniform solution. The mixtureobtained was filtered by the 0.4 μm filter to obtain a solution of thepolyamic acid resin composition of the present invention.

Using the solution of the polyamic acid resin composition prepared, auniform film was formed in a thickness of 2.0 μm in conformity withExample 1. As a result of the same evaluation, the pattern resolutionwas such that the line-and-space pattern was formed without peeling upto the width of 10 μm. The contact angles of water and methylene iodidedetermined in conformity with Example 1 were 100° and 73.3°,respectively, and the surface energy was 21.3 dyn/cm.

EXAMPLE 3

1.41 g (4.8 mmol) of 1,3-bis(4-aminophenoxy)benzene, 3.00 g (5.6 mmol)of 4-(4-perfluorooctylphenoxy)-1,3-diaminobenzene, and 1.86 g (9.5 mmol)of 1,2,3,4-cyclobutanetetracarboxylic dianhydride were made to react in35.5 g of NMP at room temperature for six hours, thereby obtaining asolution of a polyamic acid [b-2] having a number average molecularweight of 10,000 (l=17 as repeating units). The reduced viscosity of thepolyamic acid was 0.4 dl/g (in N-methylpyrrolidone at a temperature of30° C., at a concentration of 0.5 g/dl).

0.2 g of the above solution of the polyamic acid [b-2] was added into 20g of the solution of the polyamic acid [a-1] in Example 1 (solid contentratio=99:1), and 5.0 g of NMP was further added thereinto to dilute thesolution to a resin concentration of 12%. This solution was stirred atroom temperature for one hour to obtain a uniform solution. The mixtureobtained was filtered by the 0.4 μm filter to obtain a solution of thepolyamic acid resin composition of the present invention.

Using the solution of the polyamic acid resin composition prepared, auniform film was formed in a thickness of 2.0 μm in conformity withExample 1. As a result of the same evaluation, the pattern resolutionwas such that the line-and-space pattern was formed without peeling upto the width of 10 μm. The contact angles of water and methylene iodidedetermined in conformity with Example 1 were 101.2° and 76.2°,respectively, and the surface energy was 19.6 dyn/cm.

EXAMPLE 4

2 g (6.8 mmol) of 1,3-bis(4-aminophenoxy)benzene, 1.71 g (2.9 mmol) of1,3-diamino-5-benzyloxy-(1H,1H,2H,2H-heptadecafluoro)-1-decane, and 1.92g (9.8 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride were madeto react in 31.9 g of NMP at room temperature for six hours, therebyobtaining a solution of a polyamic acid [b-3] having a number averagemolecular weight of 11,000 (l=10 as repeating units). The reducedviscosity of the polyamic acid was 0.3 dl/g (in N-methylpyrrolidone at atemperature of 30° C., at a concentration of 0.5 g/dl).

0.2 g of the above solution of the polyamic acid [b-3] was added into 20g of the solution of the polyamic acid [a-1] in Example 1 (solid contentratio=99:1), and 5.0 g of NMP was further added thereinto to dilute thesolution to a resin concentration of 12%. This solution was stirred atroom temperature for one hour to obtain a uniform solution. The mixtureobtained was filtered by the 0.4 μm filter to obtain a solution of thepolyamic acid resin composition of the present invention.

Using the solution of the polyamic acid resin composition prepared, auniform film was formed in a thickness of 2.0 μm in conformity withExample 1. As a result of the same evaluation, the pattern resolutionwas such that the line-and-space pattern was formed without peeling upto the width of 10 μm. The contact angles of water and methylene iodidedetermined in conformity with Example 1 were 105° and 79°, respectively,and the surface energy was 18.4 dyn/cm.

COMPARATIVE EXAMPLE 1

Using only the solution of the polyamic acid [a-1] in Example 1, a filmwas formed in a film thickness of 2.0 μm in conformity with Example 1.As a result of the same evaluation, the pattern resolution was such thatthe line-and-space pattern was formed without peeling up to the width of10 μm. The contact angles of water and methylene iodide determined inconformity with Example 1 were 64.8° and 31.8°, respectively, and thesurface energy was 44.8 dyn/cm.

COMPARATIVE EXAMPLE 2

5.52 g (51.0 mmol) of p-phenylenediamine, 3.39 g (9.6 mmol) of4-octadecyloxy-1,3-diaminobenzene, and 18.02 g (60.0 mmol) of3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride weremade to react in 152 g of NMP at room temperature for six hours. Thesolution was diluted with NMP to a solid content of 6.0 wt %, andthereafter acetic anhydride and pyridine were added thereinto, followedby dehydration and ring closure reaction at 40° C. for two hours. Thissolution was poured into methanol and the resultant solution wassubjected to filtration and drying, thereby obtaining polyimide powderhaving a number average molecular weight of 17,000 (l=38 as repeatingunits). The reduced viscosity of the polyimide was 0.6 dl/g (inN-methylpyrrolidone at a temperature of 30° C., at a concentration of0.5 g/dl). The polyimide powder was dissolved in NMP to obtain apolyimide solution [c] having a resin concentration of 12%.

The polyimide solution [c] was mixed with the solution of polyamic acid[a-1] in Example 1 at a solid content ratio of 99:1, and the mixture wasdiluted with NMP to a resin concentration of 12%. This solution wasstirred at room temperature for one hour to obtain a uniform solution.The mixture obtained was filtered by the 0.4 μm filter to obtain asolution of the mixed resin composition.

Using the solution of the mixed resin composition prepared, a film wasformed in a thickness of 2.0 μm in conformity with Example 1. As aresult of the same evaluation, the pattern resolution was such that theline-and-space pattern was formed without peeling up to the width of 10μm. The contact angles of water and methylene iodide determined inconformity with Example 1 were 73.1° and 38.0°, respectively, and thesurface energy was 40.8 dyn/cm.

COMPARATIVE EXAMPLE 3

17.2 g (47.5 mmol) of 2,2-bis(3-amino-4-methylphenyl) hexafluoropropaneand 9.81 g (50.0 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydridewere made to react in 64.5 g of NMP at room temperature for 24 hours toobtain a solution of a polyamic acid [d] having a number averagemolecular weight of 40,000 (k=72 as repeating units). The reducedviscosity of the polyamic acid was 0.7 dl/g (in N-methylpyrrolidone, ata temperature of 30° C., at a concentration of 0.5 g/dl). The solutionof the polyamic acid obtained was filtered by the 0.4 μm filter toobtain a solution of the polyamic acid resin composition.

Using the solution of the polyamic acid resin composition prepared, afilm was formed in a thickness of 2.0 μm in conformity with Example 1.As a result of the same evaluation, the pattern resolution was such thatthe line-and-space pattern was formed without peeling up to the width of10 μm. The contact angles of water and methylene iodide determined inconformity with Example 1 were 70.8° and 39.6°, respectively, and thesurface energy was 40.5 dyn/cm.

COMPARATIVE EXAMPLE 4

13.8 g (26.6 mmol) of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 10.0 g (40.2 mmol) of1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and 12.8 g (65.5mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride were made toreact in 207 g of NMP at room temperature for six hours, therebyobtaining a solution of a polyamic acid [e] having a number averagemolecular weight of 10,000 (k=18 as repeating units). The reducedviscosity was 0.4 dl/g (in N-methylpyrrolidone, at a temperature of 30°C., at a concentration of 0.5 g/dl).

The solution of the polyamic acid [e] was mixed with the solution of thepolyamic acid [a-1] in Example 1 at a solid content ratio of 99:1, andthe mixture was diluted with NMP to a resin concentration of 12%. Thissolution was stirred at room temperature for one hour to obtain auniform solution. The mixture obtained was filtered by the 0.4 μm filterto obtain a solution of the polyamic acid resin composition.

Using the solution of the polyamic acid resin composition prepared, afilm was formed in a thickness of 2.0 μm in conformity with Example 1.As a result of the same evaluation, the pattern resolution was such thatthe line-and-space pattern was formed without peeling up to the width of10 μm. The contact angles of water and methylene iodide determined inconformity with Example 1 were 78.3° and 42.9°, respectively, and thesurface energy was 38.1 dyn/cm.

Industrial Applicability

The polyamic acid film made from the composition of the presentinvention can undergo etching with an alkali aqueous solution throughthe use of a positive type photoresist; and, through a process ofexposure with a mask having a predetermined pattern, development, andsubsequent thermal imidization, a polyimide resin with a relief patternof microscopic shape and high dimensional precision can be obtainedreadily with good adhesion to a substrate.

Since the polyimide resin has a low surface energy in the upper part offilm, it is suitable for use of a bank adapted to the ink jet method inliquid crystal displays and EL displays.

Furthermore, since the components [a] and [b] of the present inventionboth are polyamic acids, they demonstrate moderate miscibility with oneanother and it is easy to adjust the ratio of components, as comparedwith cases where different kinds of resins are blended or cases where asurfactant is added to resin.

1. A polyamic acid resin composition for the formation of a bank, whichcomprises: a polyamic acid having repeating units represented by formula

wherein R¹ is a tetravalent organic group derived from a tetracarboxylicacid or a derivative thereof, R² is a bivalent organic group derivedfrom a diamine, and k is an integer[)], and having a reduced viscosityranging from 0.05 to 5.0 dug [(] as determined in N-methylpyrrolidone ata temperature of 30° C., at a concentration of 0.5 gl/g[)]; and apolyamic acid (b) having repeating units represented by formula

wherein R³ is a tetravalent organic group derived from a-tetracarboxylicacid compound or a derivative thereof, R⁴ is a bivalent organic groupderived from a diamine compound, from 1 to 100 mol % of R⁴ has one ormore fluorine-containing alkyl groups with a carbon number of at least2, and 1 is an integer[)], and having a reduced viscosity ranging from0.05 to 5.0 dl/g [(] in N-methylpyrrolidone at a temperature of 30° C.,at a concentration of 0.5 g/dl[)]; wherein the content of the polyamicacid (b) ranges from 0.1 to 30 wt % based on the total amount of thepolyamic acid (a) and the polyamic acid (b).
 2. The polyamic acid resincomposition according to claim 1, wherein R¹ in formula (1) is atetravalent organic group derived from1,2,3,4-cyclobutanetetracarboxylic acid or a derivative thereof.
 3. Thepolyamic acid resin composition according to claim 1 or 2, wherein R³ informula (2) is a tetravalent organic group derived from1,2,3,4-cyclobutanetetracarboxylic acid or a derivative thereof.
 4. Thepolyamic acid resin composition according to claim 1, wherein, through aprocess of applying a positive type resist onto a film of the polyamicacid resin composition, exposing the resist and film to light through amask, performing development thereof with an alkali developer, removingthe resist, and heating the film until it converts into a polyimideresin, the upper part of the unexposed portion of the polyimide resinfilm has a surface energy of at most 35 dyn/cm.
 5. The polyamic acidresin composition according to claim 1, wherein, through a process ofapplying a positive type resist onto a film of the polyamic acid resincomposition, exposing the resist and film to light through a mask,performing development thereof with an alkali developer, removing theresist, and heating the film until it turns into a polyimide resin, theupper part of the unexposed portion of the polyimide resin film has acontact angle with water of at least 80°.
 6. The polyamic acid resincomposition according to claim 1, wherein the tetracarboxylic acidderivative which provides the tetravalent organic groups R¹ and R³ ofthe polyamic acids of formulas (a) and (b) is an aromatictetracarboxylic dianhydride selected from the group consisting ofpyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-diphenylether tetracarboxylic dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and3,3′,4,4′-diphenyl sulfone tetracarboxylic dianhydride.
 7. The polyamicacid resin composition according to claim 1, wherein the tetracarboxylicacid derivative which provides the tetravalent organic groups R¹ and R³of the polyamic acids of formulas (a) and (b) is an alicyclictetracarboxylic dianhydride selected from the group consisting of1,2,3,4-cyclobutanetetracarboxlic dianhydride,1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,3,5-cyclohexanetetracarboxylic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride,2,3,5-tricarboxy-2-cyclopentaneacetic dianhydride,bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic dianhydride and3,5,6-tricarboxy-2-norbornaneacetic dianhydride or1,2,3,4-butanetetracarboxylic dianhydride as an aliphatictetracarboxylic dianhydride.
 8. The polyamic acid resin compositionaccording to claim 1, wherein the diaxnine compound which provides thedivalent organic group R² of the polyamic acid of formula (a) isp-phenylenediamine, m-phenylenediamine,4,4-methylene-bis(2,6.ethylaniline),4,4′-methylene-bis(2isopropyl-6-methylaniline),4,4′-methylene-bis(2,6-diisopropylaniline),2,4,6-trimethyl-1,3-phenylenediamine,2,4,5,6-tetramethyl-1,4-phenylenediamine,o-toluidine, m-toluidine,3,3′,5,5′-tetramethylbenzidine, bis[4-(3aminophenoxy)phenyl]sulfone,2,2-bis[4-(3-aminophenoxy)phenyl]propane,2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane,4,4′-diamino-3,3′-dimethyldicyclohexylmethane, 4,4′-diaminodiphenylether, 3,4-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane,2,2-bis(4anilino)hexafluoropropane, 2,2bis(3anilino)hexafluoropropane,2,2-bis(3-amino-4-toluyl)hexafluoropropane,1,4bis(4aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,bis[4-(4aminophenoxy)Phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)Phenyl]propane and2,2-bis[4(4aminophenoxy)phenyl]hexafluoropropane.
 9. The polyamic acidresin composition according to claim 1, wherein the diamine compoundwhich provides the divalent organic group R⁴ component of the polyamicacid of formula (b) that contains the fluorine-containing alkyl group is4-trifluoroethyl-1,3-diaminobenzene,4-perfluorohexyl-1,3-diaminobenzene, 4-perfluorooctyl-1,3diaminobenzene,4-perfluorohexyl-1,3-diaminobenzene,5-(2,2,3,3,3-pentafluoropropyl-1-oxymethyl)-1,3-diaminobenzene,5-(1H,1H,2H,2H-heptadecafluorodecyl-1-oxymethyl)-1,3diaminobenzene,4perfluorodecyl-1,3diaminobenzene,2,2,3,3,3pentafluoropropyl-3,5-diaminobenzoate, 1H,1H,2H,2H-heptadecafluorodecyl-3,5-diaminobenzoate and4-(4-perfluorooctylphenoxy)-1,3diaminobenzene.
 10. The polyamic acidresin composition according to claim 1, wherein the content of bivalentradicals that are derived from diamine compounds containing one or morefluorine-containing alkyl groups with a carbon number of at least 2 thatconstitute radical R⁴ ranges from 25 to 75 mol %.
 11. The polyamic acidresin composition according to claim 1, wherein the diamine compoundwhich provides the divalent organic group R² of the polyamic acid offormula (a) is a siloxane-containing diaxnine of the formula:

wherein p is an integer from 1 to
 10. 12. The polyamic acid resincomposition according to claim 1, wherein the polyamic acid of formula(a) has a reduced viscosity ranging from 0.2 to 2.0 dl/g.
 13. Thepolyamic acid resin composition according to claim 1, wherein thepolyamic acid of formula (b) has a reduced viscosity ranging from 0.1 to1.5 dl/g.